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<h4 class="subsection" id="x86-Control_002dFlow-Protection-Intrinsics"><span>6.60.37 x86 Control-Flow Protection Intrinsics<a class="copiable-link" href="#x86-Control_002dFlow-Protection-Intrinsics"> &para;</a></span></h4>

<dl class="first-deftypefn">
<dt class="deftypefn" id="index-_005fget_005fssp"><span class="category-def">CET Function: </span><span><code class="def-type">ret_type</code> <strong class="def-name">_get_ssp</strong> <code class="def-code-arguments">(void)</code><a class="copiable-link" href="#index-_005fget_005fssp"> &para;</a></span></dt>
<dd><p>Get the current value of shadow stack pointer if shadow stack support
from Intel CET is enabled in the hardware or <code class="code">0</code> otherwise.
The <code class="code">ret_type</code> is <code class="code">unsigned long long</code> for 64-bit targets 
and <code class="code">unsigned int</code> for 32-bit targets.
</p></dd></dl>

<dl class="first-deftypefn">
<dt class="deftypefn" id="index-_005finc_005fssp"><span class="category-def">CET Function: </span><span><code class="def-type">void</code> <strong class="def-name">_inc_ssp</strong> <code class="def-code-arguments">(unsigned int)</code><a class="copiable-link" href="#index-_005finc_005fssp"> &para;</a></span></dt>
<dd><p>Increment the current shadow stack pointer by the size specified by the
function argument.  The argument is masked to a byte value for security
reasons, so to increment by more than 255 bytes you must call the function
multiple times.
</p></dd></dl>

<p>The shadow stack unwind code looks like:
</p>
<div class="example smallexample">
<pre class="example-preformatted">#include &lt;immintrin.h&gt;

/* Unwind the shadow stack for EH.  */
#define _Unwind_Frames_Extra(x)       \
  do                                  \
    {                                \
      _Unwind_Word ssp = _get_ssp (); \
      if (ssp != 0)                   \
        {                            \
          _Unwind_Word tmp = (x);     \
          while (tmp &gt; 255)           \
            {                        \
              _inc_ssp (tmp);         \
              tmp -= 255;             \
            }                        \
          _inc_ssp (tmp);             \
        }                            \
    }                                \
    while (0)
</pre></div>

<p>This code runs unconditionally on all 64-bit processors.  For 32-bit
processors the code runs on those that support multi-byte NOP instructions.
</p>
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